The present invention relates to detection of fan speed and/or fan failure.
It is often desirable to provide a mechanism for automatically determining the speed of a fan, such as a fan used to cool electronic equipment, and/or to determine when the fan has failed, i.e., slowed down or stopped. One possible approach is to monitor the fan speed by sensing the rate at which an optical path is interrupted by the fan blades. Another approach is to monitor the fan speed by using a hall effect device to sense the rate at which the magnetic field created by the fan motor is rotating. Yet another approach, applicable principally only to fan failure, is to monitor the cooling airflow via a sail switch.
Each of these (and other) approaches has some disadvantage(s), however. For example, the sail switch needs to be delicately adjusted and, because it is a mechanical device, it is relatively unreliable. In addition, it will interfere with the airflow to some extent. A disadvantage of the optical approach is that the optical paths are subject to blockage. A disadvantage of the hall effect approach is that the hall effect device must be installed when the fan is manufactured. Thus such an arrangement is not readily retrofitted into existing installations. Moreover, stray magnetic fields may affect its operation.